But if ye had known what this meaneth, I will have mercy, and not sacrifice, ye would not have condemned the guiltless. I will have mercy, etc. - See this explained, Matthew 9:13.
There are four ways in which positive laws may cease to oblige.
First, by the natural law of necessity.
Secondly, by a particular law, which is superior.
Thirdly, by the law of charity and mercy.
Fourthly, by the dispensation and authority of the Lawgiver.
These cases are all exemplified from Matthew 12:4-8.